1. Field of the Invention
This invention relates to multi-ply paper formation. More specifically, this invention relates to two-wire, multi-ply paper formation. Still more particularly, this invention relates to two-wire, multi-ply web formation wherein the outer ply to be ply-bonded to the base ply of the multi-ply web, has its surface dewatered essentially by wire tension and centrifugal force.
1. Description of the Prior Art
In prior forming arrangements for forming a multi-ply paper web product, a relatively coarse base ply is first produced and a second, outer ply is produced to be brought into ply-bonding contact with the previously formed base ply. The outer ply, which is intended to form the outer surface of a printed container, such as a box, is formed of a finer grade of pulp stock so as to provide a smoother, higher quality surface. In order to form the outer ply at commercially desirable speeds, dewatering was effected through both of its surfaces before the outer ply was brought into ply-bonding contact with the base ply of the paper web sheet. This produces an acceptable paper product, mainly due to the quality of the pulp stock used to produce the outer ply, but the requirements of producing a better product with cheaper pulp, and the need to produce a better product at higher speeds regardless of pulp quality, or a combination of both, have necessitated the conception of an improved multi-ply web former having an outer surface which exhibits the desired printability, and feel and visual smoothness while having an inner surface which has better ply-bonding characteristics.
In prior apparatus, both sides of the outer ply were dewatered positively, that is, they were dewatered by the application of sub-atmospheric air pressure directly to both surfaces to enhance the removal of water through both of the web surfaces. When both surfaces are positively dewatered, fines and fillers in the pulp stock are urged outwardly in both directions to the respective surfaces of the web and removed during the dewatering process. Thus, while the web is rapidly dewatered, which was the desired effect, the fines and fillers which contribute so much to the ply bonding characteristics of the outer side of the web produced, were removed in large quantities which deleteriously effected web quality as well.